CN107482323B - Terahertz waveband multilayer metamaterial broadband wave absorber - Google Patents
Terahertz waveband multilayer metamaterial broadband wave absorber Download PDFInfo
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- CN107482323B CN107482323B CN201710692986.7A CN201710692986A CN107482323B CN 107482323 B CN107482323 B CN 107482323B CN 201710692986 A CN201710692986 A CN 201710692986A CN 107482323 B CN107482323 B CN 107482323B
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- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q17/00—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems
- H01Q17/008—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems with a particular shape
Abstract
The invention relates to a terahertz waveband multilayer metamaterial broadband wave absorber. The metamaterial wave absorber is formed by overlapping a single-layer broadband wave absorber and an island-shaped structure. The single-layer wave absorber is composed of a sandwich structure of metal pattern, dielectric medium and metal bottom plate. The metal pattern is formed by arranging four open resonant rings with the same size, and the only difference between the open resonant rings is the difference of the bottom heights. The single-layer wave absorber can have nearly perfect absorptivity and larger full width at half maximum after the parameters are properly optimized. And continuously superposing the island structures on the basis of the single-layer wave absorber unit, and covering each island structure right above the split resonant ring. The island structure has little influence on the original absorption peak, and a new absorption peak can be added near a high-frequency band to expand the bandwidth. The wave absorber with the island-shaped structure has extremely large relative bandwidth which is far higher than the synchronous level, and has wide application prospect.
Description
Technical Field
The invention relates to a metamaterial broadband wave absorber, and belongs to the field of artificial electromagnetic materials.
Background
The metamaterial has received great attention from the beginning of development because it has many unusual characteristics that are difficult to obtain in nature, such as negative refractive index, negative electrical conductivity, negative magnetic permeability, and the like. Moreover, the LED lamp is rapidly developed due to the characteristics of easy integration, small size, thin thickness and the like. The associated devices then begin to emerge.
In 2008, Landy et al demonstrated a metamaterial wave absorber for the first time, which can achieve perfect absorption of electromagnetic waves at a single frequency point, and further arouse the interest of numerous scientists due to the many advantages of metamaterials. To further broaden the applications, the development of multiband or broadband absorbers has become a trend today. For a broadband wave absorber, how to realize an ultra-wide absorption band and ensure a high absorption rate is a difficult point to be solved urgently. The multilayer metamaterial broadband wave absorber provided by the invention can absorb more than 90% of electromagnetic wave energy within the range of 1.23-4.74 Thz, and can keep high-efficiency absorption capacity under an oblique incidence angle of 60 degrees, so that the multilayer metamaterial broadband wave absorber has extremely high potential application value.
Disclosure of Invention
The invention aims to solve the problems of narrow frequency band, low absorption rate and the like of a metamaterial wave absorber, provides a terahertz wave band multilayer metamaterial broadband wave absorber capable of working under a wide incident angle, and can change the absorption bandwidth to a certain extent by adjusting size parameters.
The technical scheme of the invention is as follows:
a terahertz waveband multi-layer metamaterial broadband wave absorber is formed by periodically extending wave absorbing units. The wave absorbing unit is square in outline and comprises a bottom metal plate, a first dielectric layer and four split resonance rings.
The upper surface and the lower surface of the first dielectric layer are respectively attached to the lower surfaces of the four open resonant rings and the upper surface of the bottom metal plate, so that a single-layer dielectric broadband wave absorber with a sandwich structure is formed.
The four split ring resonators are distributed on the dielectric layer in an array mode, the sizes of the four split ring resonators are the same, the directions of the split rings are the same, the height of the bottom of the four split ring resonators is increased from the first split ring resonator to the fourth split ring resonator in a clockwise mode, and other dimensional parameters are the same.
By adopting the wave absorber with the structure, more than 90 percent of electromagnetic wave energy can be absorbed in the range of 1.23-4.74 Thz, and 3 different absorption peaks are shown. The 3 absorption peaks mainly originate from the sandwich structure of open resonator ring-dielectric layer-metal back plane and mainly from ohmic losses. Because the wave absorber formed by the single open resonant ring can form an absorption peak at a certain frequency, the absorption frequency can be influenced by changing the height of the bottom, and after 4 open resonant rings are added, a plurality of absorption peaks with closer absorption frequencies are overlapped and act together to form three closer absorption peaks, and then the broadband characteristic is displayed.
Furthermore, an island-shaped structure is covered right above the four split ring resonators respectively; the island structure comprises a second dielectric layer, a first metal block, a third dielectric layer and a second metal block; the second dielectric layer vertically covers the open resonant ring and keeps consistent with the length and width of the open resonant ring; and sequentially stacking a first metal block, a dielectric layer and a second metal block right above the second dielectric layer, wherein the metal block and the metal block are identical and are consistent with the length and the width of the dielectric layer. The second dielectric layer and the third dielectric layer are of similar thickness.
The invention excites the first-order magnetic response above the open resonant ring through the superposed island structure to obtain a new absorption peak, namely the 4 th absorption peak, which comes from the dielectric loss of the dielectric layer. Therefore, the combined action of ohmic loss and dielectric loss converts the absorbed electromagnetic energy into heat energy, so that the bandwidth is effectively increased, and the effect of absorbing waves by the broadband is realized. The absorption peak generated by the island-shaped structure is mainly shown in the fourth peak, and the first three absorption peaks are slightly influenced, so that the whole structure still can keep high absorptivity, and the island-shaped structure can be better suitable for other similar single-layer wave absorber structures to widen the bandwidth.
Adopt above-mentioned technical scheme's beneficial effect to lie in:
1. the invention can realize high absorptivity by applying four open resonant rings with the same length and width but different bottom heights. Because only single parameters among the resonators are changed without changing the whole size, the design thought is widened.
2. The invention adopts a superposed island structure of the resonator to excite first-order magnetic response to obtain a new absorption peak, thereby effectively increasing the bandwidth. The absorption peak generated by the island structure is mainly shown in the fourth peak, and has a small influence on the first three absorption peaks, so that the high absorptivity can still be maintained as a whole. And can be better suitable for other similar single-layer wave absorber structures to widen the bandwidth.
3. The wave absorber formed by the invention can absorb more than 90% of electromagnetic wave energy within the range of 1.23-4.74 Thz, has the full width at half maximum of 139.7%, is much higher than other structural types of wave absorbers, and shows 4 different absorption peaks. The first three absorption peaks are mainly due to ohmic losses on the open resonator loop and the 4 th absorption peak is due to dielectric losses on the island structure, which in combination result in a very large absorption rate and bandwidth.
4. The multilayer metamaterial broadband wave absorber formed by the invention also shows good wave absorbing performance under an extremely wide incident angle.
5. The invention can be regarded as 4 sub-unit cells, and simplifies the design and manufacture difficulty to a certain extent.
Drawings
FIG. 1 is a schematic structural diagram of a terahertz waveband multilayer metamaterial broadband wave absorber provided by the invention;
FIG. 2(a) is a schematic structural diagram of a terahertz waveband multilayer metamaterial broadband wave absorber unit provided by the invention;
FIG. 2(b) is a side view of a terahertz waveband multilayer metamaterial broadband wave absorber unit structure provided by the invention;
FIG. 3(a) is a schematic diagram of a single-layer dielectric absorber based on a multi-layer metamaterial broadband absorber, namely, the island structure (4) is removed;
FIG. 3(b) is a schematic diagram of a unit structure of a single-layer dielectric absorber after removing the island structure (4) according to the present invention;
fig. 4(a) is an absorption spectrum diagram of a multilayer metamaterial broadband absorber according to the present invention;
FIG. 4(b) is a combined absorption spectrum diagram of the island-shaped structure (4) only, the split ring resonator (3) only and the complete structure;
FIG. 5 is a graph of absorption spectra of a multi-layered metamaterial broadband absorber under an oblique incident angle according to the present invention;
the reference signs are:
1-metal base plate; 2-a first dielectric layer; 3-open resonant ring; 4-island structure;
3-1-a first open resonant ring, 3-2-a second open resonant ring, 3-a third open resonant ring, 3-4-a fourth open resonant ring, wherein the height from the first open resonant ring to the fourth bottom is increased progressively;
4-second dielectric layer, 4-3-first metal block, 4-2-third dielectric layer and 4-1-second metal block.
Detailed Description
For a better illustration of the design process and purposes, the present invention will be further described with reference to the accompanying drawings.
To achieve this absorption performance, the present invention consists of multiple absorption cells, each absorber cell is square as shown in fig. 1, and the period extends in the x, y directions to form a complete terahertz broadband absorber with period P = 26 ~ 46 um.
As shown in fig. 2(a), the configuration of each unit is identical and is from bottom to top: bottom metal plate 1, dielectric layer 2, four split ring resonators 3, 4 island structures 4.
As shown in fig. 2(b), the metal base plate 1 at the lowest layer can be one of chromium, gold, silver, copper, etc., but in any case, the thickness must be much larger than the skin depth of the electromagnetic wave, and the thickness of the metal base plate is between 0.2 ~ 2 um.
Located above the bottom metal plate 1 is a first dielectric layer 2 having a thickness of between 8 ~ 18 um.
Four open resonator rings 3 are attached directly above the dielectric 2 as shown in fig. 3(a) fig. 3(b) shows a cell structure each cell can be seen as 4 subunits and there is one open resonator ring 3 in the center of each subunit the bottom height of the first open resonator ring 3-1 to the fourth open resonator ring 3-2 increases in sequence from clockwise to clockwise, the increasing step is between 1 ~ 3 um, the 4 open resonator rings differ only in bottom height, the other parameters are set exactly the same, the opening direction is the same, the thickness of the 4 open resonator rings 3 is between 0.05 ~ 1 um, the open resonator rings 3 are L1=12 ~ 18um long, L2= 8 ~ 16um wide, the opening width g = 0.5 ~ 4 um, the side arm width w = 0.5 ~ 2um wide, and the first open resonator ring 3-1 bottom height h1= 0.2 ~ 2 um.
The single-layer wave absorber has nearly perfect absorption rate and larger full width at half maximum after proper parameter optimization.
Four island structures 4 are further stacked on the basis of the structure shown in fig. 3(a), and the four island structures 4 are identical. The island structure has little influence on the original absorption peak, and a new absorption peak can be added near a high-frequency band to expand the bandwidth. The wave absorber with the island-shaped structure has extremely large relative bandwidth which is far higher than the synchronous level, and has wide application prospect.
Each island 4 is covered directly above the open resonator ring 3, and the resulting structure is shown in fig. 2(a) and 2(b), i.e. the island 4 is also located at the center of the subunit, and is only in the upper-lower relationship with the open resonator ring 3, although the 4 islands 4 may be optionally offset, but preferably located at the center.
The island-shaped structure 4 is sequentially a second dielectric layer 4-4, a first metal block 4-3, a third dielectric layer 4-2 and a second metal block 4-1 from bottom to top, wherein the thicknesses of the second dielectric layer 4-4, the third dielectric layer 4-2 and the second dielectric layer 4-2 are between 6 ~ 12um, the length and the width of the second dielectric layer 4-4 are consistent with those of the open resonant ring 3, the first metal block 4-3, the third dielectric layer 4-2 and the second metal block 4-1 are all rectangular, the length and the width are the same, and the length s1 of the island-shaped structure is smaller than the value of (L1-2 w), (L1-2 w) is the length of the rectangular open resonant ring, and the width s2=3 ~ 7 um.
The first dielectric layer 2, the second and third dielectric layers 4-4 and 4-2 are all lossy dielectric materials. The second and third dielectric layers 4-4 and 4-2 are polyimide with the same concentration and dielectric constantε= 3(1 +i0.06) and has a dielectric constant close to that of the first dielectric layer 2.
The second dielectric layer 4-4 is used to separate the open-ended resonant ring 3 from the metal plate on the island-shaped structure 4, so as to reduce the coupling between the open-ended resonant ring and the metal plate as much as possible, avoid damaging the resonant mechanism of the open-ended resonant ring 3, and protect the wave-absorbing capability of the sandwich structure shown in fig. 3(a) and 3 (b).
In the island-shaped structure 4 of the present embodiment, the first metal block 4-3, the third dielectric layer 4-2 and the second metal block 4-1 can be regarded as a sandwich structure, and strong first-order magnetic resonance is generated in the third dielectric layer 4-2, so that a new absorption peak is generated, a larger bandwidth is formed together with the absorption peaks generated by the original structures shown in fig. 3(a) and 3(b), and the absorbed electromagnetic waves are converted into heat energy and consumed.
The absorptivity of the terahertz waveband multilayer metamaterial broadband wave absorber can be publicly usedCalculating the formula: 1-R-T-1-S11|2- |S21|2Wherein R is the reflectance and T is the transmittance. To maximize the absorption, it is desirable to reduce T and R as much as possible over the entire frequency range. Because the thickness of the bottom layer metal plate is far larger than the skin depth, T =0, as long as the resonance structure is designed as reasonably as possible, the normalized impedance can be approximate to 1, the normalized impedance is matched with the external free space, the reflectivity is approximate to 0, and finally the nearly perfect absorption performance is generated.
The simulation result of this embodiment at normal incidence of electromagnetic waves is shown in fig. 4(a), and is calculated by the finite integration method. As can be seen from the figure, the absorbance is greater than 90% between 1.23 Thz and 4.74 Thz, and there are 4 distinct absorption peaks. The absorbances of the four absorption peaks at 1.91 Thz, 2.54 Thz, 3.38 Thz and 4.45 Thz reach 98.92%, 98.11%, 99.97% and 99.32%, respectively. Then, the island structure 4 and the split ring 3 are removed respectively to see a comparative absorption spectrum, as shown in FIG. 4 (b). It can be seen that the first three peaks are mainly associated with the open resonator ring (3) and the 4 th peak is mainly determined by the island structure 4.
The absorption of the embodiment under the oblique incidence angle is shown in fig. 5, the oblique incidence angle refers to the angle of the wave vector of the incident wave deviating from the normal line of the surface of the wave absorbing body, and as can be seen from the figure, the wave absorbing performance is good when the incidence angle is within the range of 0 ~ 60 degrees, namely, the wave absorbing material can be applied under the condition of wide-angle incidence and is more suitable for practical application.
The above is merely a preferable embodiment of the present application, the present invention is not limited to the above embodiment, and various modifications and variations of the present invention are intended to be included in the present invention if they do not depart from the spirit and scope of the present invention, provided they fall within the scope of the claims and equivalent technology of the present invention.
Claims (9)
1. A terahertz waveband multi-layer metamaterial broadband wave absorber is formed by periodically extending wave absorbing units in the x and y directions; the method is characterized in that: the wave-absorbing unit is square in outline and comprises a bottom metal plate (1), a first dielectric layer (2) and four open resonant rings (3);
the upper surface and the lower surface of the first dielectric layer (2) are respectively attached to the lower surfaces of the four open resonant rings (3) and the upper surface of the bottom metal plate (1) to form a single-layer dielectric broadband wave absorber with a sandwich structure;
the four split ring resonators (3) are distributed on the dielectric layer (2) in an array mode, are identical in size and opening direction, and increase the bottom height from the first split ring resonator (3-1) to the fourth split ring resonator (3-4) in sequence according to the clockwise direction, and other dimensional parameters are identical;
an island-shaped structure (4) is covered right above the four split resonant rings (3);
the island-shaped structure (4) comprises a second dielectric layer (4-4), a first metal block (4-3), a third dielectric layer (4-2) and a second metal block (4-1); the second dielectric layer (4-4) vertically covers the open resonant ring (3) and keeps consistent with the length and width of the open resonant ring; sequentially stacking a first metal block (4-3), a third dielectric layer (4-2) and a second metal block (4-1) right above the second dielectric layer (4-4), wherein the first metal block (4-3) and the second metal block (4-1) are completely the same and are consistent with the shape of the third dielectric layer (4-2); the second dielectric layer (4-4) and the third dielectric layer (4-2) have similar thicknesses.
2. The terahertz waveband multilayer metamaterial broadband absorber of claim 1, wherein the structure formed by the first metal block (4-3), the third dielectric layer (4-2) and the second metal block (4-1) of the four island structures uniformly selects a central position or an offset position on the second dielectric layer (4-4).
3. The terahertz waveband multilayer metamaterial broadband absorber of claim 2, wherein: the shape of the first metal block (4-3), the third dielectric layer (4-2), and the second metal block (4-1) on the island structure is one of rectangular, circular, and square.
4. The terahertz waveband multilayer metamaterial broadband absorber of claim 1 or 2, wherein: the bottom metal plate (1), the four open-ended resonant rings (3), the first metal block and the second metal block are all made of metal, one of chromium, gold, silver, copper and the like is selected, preferably chromium, and the conductivity isσ=2.2 × 105S/m。
5. The terahertz waveband multilayer metamaterial broadband wave absorber as claimed in claim 1 or 2, wherein the thickness of the bottom metal plate (1), the four open-ended resonant rings (3), the first metal block and the second metal block is far larger than the skin depth, and the thickness is between 0.2 ~ 2 um.
6. The terahertz wave band multilayer metamaterial broadband wave absorber as claimed in claim 1 or 2, wherein the period p of the wave absorbing unit is 26 ~ 46 um.
7. The terahertz waveband multilayer metamaterial broadband wave absorber as claimed in claim 1 or 2, wherein the dielectric layers are all 6 ~ 18um thick and made of polymer or oxide.
8. The terahertz waveband multilayer metamaterial broadband absorber of claim 7, wherein: the third dielectric layer (4-2) and the second dielectric layer (4-4) are made of polyimide and have a dielectric constant ofε= 3(1 +i0.06); the first dielectric layer (2) is also polyimide, preferably with a refractive index of 1.68 + i 0.06.
9. The terahertz waveband multilayer metamaterial broadband absorber as claimed in claim 1 or 2, wherein the thickness of each of the four open resonant rings (3) is 0.05 ~ 1 um, the length of each open resonant ring (3) is L1=12 ~ 18um, the width of each open resonant ring is L2= 8 ~ 16um, the width of each open resonant ring is g = 0.5 ~ 4 um, the width of each side arm is w = 0.5 ~ 2um, the height of the bottom of the first open resonant ring (3-1) is h1= 0.2 ~ 2um, and the heights of the bottoms of the second open resonant ring (3-2) to the fourth open resonant ring (3-4) are sequentially increased by 1 ~ 3 um.
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